This issue is documented in readme for BDS2006. This is the note from BDS 2006's readme file:

C++ NotesIf you are creating a C++ Package that contains a Delphi unit thatuses the DesignIntf and DesignEditors tools, you must choose Project|Options|Pascal Compiler|Other Options and then add "-LUDesignIDE" for the compiler to work correctly.

So in CB2007/RAD Studio 2007, all you need to do is:

Project|Options|Pascal Compiler|Other Options|"Use these packages whencompiling", then add "DesignIDE" in the combobox.